This invention relates to overtension release web cutters particularly for use with high speed web transport machines, such as used in the manufacture or processing of photographic film, paper manufacturing, and printing. In such machinery, failures may occur in the web path control due to loss of electrical power, machinery jams or defective webs. Such failures can result in tension transients propagated through the web which may damage machine tooling by, for instance, bending roller shafts and misaligning or breaking punches. Some webs, particularly webs of polyester film, exhibit extremely high tensile strength and tear or break/snap only at tension exceeding hundreds of pounds per inch width of product.
Web severing devices are known in the printing industry, particularly in association with high speed printing presses. Such devices are designed to sever a paper web to prevent torn portions of the web from continuing into the press and thus prevent damage to such press. Web severing action is initiated either by an operator manually tripping a switch, or automatically in response to a signal received from a web break detector located along the web path.
One such web severing device is described in U.S. Pat. No. 3,881,383. The device includes a pair of rollers mounted on a press on opposite sides of the web. The upper roller has a fixed axis of rotation. The lower roller is movable, by a pneumatic device, in an up and down fashion toward and away from the upper roller. In the preferred embodiment the lower roller carries a severing blade which always protrudes beyond the outer cylindrical surface of such roller. Upon being triggered, preferably by a web break detector, the lower roller is forced upward by the pneumatic device into engagement with the web. Thereupon the motion or momentum of the web is utilized to rotate the lower roller and swing the cutting blade into engagement with the web to sever the web. Column 5, lines 18-21 of the patent indicates the blade could be mounted on the stationary roller instead of the movable roller.
Solenoid actuated guillotine cutters are also known in the film industry. However, in equipment such as spoolers and slitters where the film is traveling at high speeds (for instance 2000 ft./min.), the time it takes to detect an overtension condition in the film, then actuate the solenoid, and then for the cutter to sever the web may not be fast enough to prevent damage to the machine. In fact detectors and solenoid actuators may be inoperable if the tension transient results from an electrical failure in the machine.